Apoptosis, also called the process of programmed cell death, is thought to play an important role in anticancer therapy. Strategies of inducing apoptosis as well as inhibiting abnormal cell proliferation are developed for anti-cancer therapy. Doxorubicin (DXR), one of the most well-known anti-cancer agents, could induce apoptosis in rat hepatoma cells (AH66). After 24 h of drug treatment, DNA fragmentation of the cells was observed within 15 h, along with an increase in caspase-3 activity. Intracellular caspase-3 activity is thought to be correlated well with the ability to induce DNA fragmentation (Asakura et al., Br. J. Cancer 1999, 80, 711-715).
A telomere is a region of repetitive DNA sequence at the end of a chromosome that protects the end of the chromosome from deterioration or fusion with neighboring chromosomes. In normal somatic cells, telomeres become shortened each time the cells divide via mitosis. There is growing evidence that accelerated telomere attrition and/or aberrant telomerase activity contribute(s) to pathogenesis in a number of diseases and may also increase cellular survival by conferring resistance to apoptosis (Bermudez et al., Clin. Interv. Aging 2006, 1, 155-167). Furthermore, the expression of human telomerase reverse transcriptase (hTERT) reduces activation of caspases 3, 8, and 9, reduces pro-apoptotic mitochondrial proteins t-BID, BAD, and BAX and increases anti-apoptotic mitochondrial protein, Bcl-2. The ability of telomerase to suppress caspase-mediated apoptosis is p-JNK-dependent since abrogation of JNK expression with JIP abolishes resistance to apoptosis. Reductions in hTERT mRNA expression level and telomerase activity are observed during the processes of cellular aging or immortalization (Bestilny et al., Cancer Res. 1996, 56, 3796-802). Still, the level of telomerase activity in somatic cells, which is undetectable at the basal level, could be heightened by induction of hTERT cDNA (Bodnar et al., Science. 1998, 279, 349-52).
Telomeres in eukaryotic cells are guanine-rich. Under normal physiological conditions, single-strand DNA of the telomeres will spontaneously form a G-quadruplex structure. The G-quadruplex structure includes two portions in which one is a small loop composed of TTA, and the other a guanine-tetrad composed of four guanines formed by cyclic hydrogen bonds. Because of the role telomerase plays in cellular aging and apoptosis, direct inhibition of telomerase activity can be used to block the differentiation of tumor cells. Similarly, stabilizing the G-quadruplex structure to inhibit its complementation with the single strand RNA (AAUCCC) can also prevent telomere extension, thereby inhibiting cell proliferation. In short, inhibition of chromosome replication via either inhibition of telomerase or stabilization of the G-quadruplex offers a potential strategy for inhibiting tumor cell growth (Smogorzewska et al., Annu. Rev. Biochem. 2004, 73, 177-208).
Induction of apoptosis or inhibition of telomerase activity by anti-cancer agents has been shown to correlate with tumor suppression; however, non-apoptotic forms of cell death, such as autophagy and extrinsic senescence, have also been shown to contribute to the overall tumor response. Cellular damage induces growth arrest and tumor suppression by inducing apoptosis, necrosis, senescence and the expression of p53; the mechanism of cell death depends on the magnitude of DNA damage following exposure to various concentrations of anti-cancer agents. p53 is a transcription factor that activates vital damage containment procedures to restrict aberrant cell growth in response to DNA damage, oncogene activation, hypoxia and the loss of normal cell contacts (Giaccia and Kastan, Denes Dev. 1998, 12, 2973-2983; Lohrum and Vousden, Cell Death Differ. 1999, 6, 1162-1168). p53 restricts cellular growth not only by inducing a non-apoptotic mechanisms involved in senescence, cell cycle arrest (at G1 and/or G2 phase) but also by inducing apoptotic mechanisms (Jin and Levine, J. Cell Sci. 2001, 114, 4120-4139). p53 is also reported to be able to work coordination with p21 for noscapine-mediated apoptosis (Aneja et al., Cancer Res. 2007, 67, 3862-3870). In addition, Apoptosis-resistant cells and transduction pathways which inhibit apoptosis can induce non-apoptotic mechanisms of cell death and senescence, thereby preserving the antitumor effect of some anticancer agents (Kim et al., Cancer Biol. Ther. 2006 11, 1429-1442), implicating a potentially-flexible strategy for inhibiting cancer cell proliferation and inducing apoptosis.
It is known that over-expression of known oncogenes usually induces cancers. It is also known that over-expression of these genes is also associated with many cell proliferation disorders, such as chronic lymphocytic leukemia, esophagus cancer, myeloma, etc. Moreover, many experiments have shown that over-expression of tumor suppressor genes can play an important role in the prevention and treatment of tumors, thereby, establishing the connection between cancer and cell proliferation disorders. Therefore, research and development on drugs for curing cell proliferation disorders, such as telomerase inhibitors, can be applied to the treatment of human cancers, as taught in the disclosures of Canadian Patent No. 2,428,206.
Although quite a few strategies associated with inducing apoptosis and inhibiting cell proliferation via telomerase inhibition could be surmised based on the foregoing knowledge, no report has been made to date for any substances with unambiguously effective said strategies and properties satisfactory for pharmaceutical use.